Pull type harvesting implements have been utilized for various harvesting operations for many years. These harvesting implements, supported primarily by ground engaging wheels, are made in a variety of configurations, but normally include components supported on a transverse frame to which is connected a pivotal draft member, commonly called a drawbar or draft tongue. For convenience, any draft member discussed in the following description will be referred to as a tongue.
In pull type harvesters, the tongue extends forwardly of the transverse frame for attachment to a prime mover, such as a tractor, which pulls the implement and provides operative power for various harvesting components supported by the main frame. For example, if the implement is a mower-conditioner, cutting and conditioning components mounted on the frame require operative power, which is provided mechanically or hydraulically by the tractor. Hydraulic drive systems are costly and have been fraught with operational problems, not the least of which is power limitations when large implements are involved. Thus, in light of such problems implement designers have turned to the use of a mechanical drive line between the tractor and the harvester.
U.S. Pat. Nos. 4,187,664, issued Feb. 12, 1980 in the name of Nigel W. Meek, et al, and No. 5,172,539, issued Dec. 22, 1992 in the name of Richard E. Jennings, et al, show examples of prior art pull type harvesting implements having a pivotal tongue and a mechanical drive system for providing operative power to conventional cutting and conditioning components mounted on a frame. In the implement shown in the '664 patent the tongue pivots about a vertical axis located at the left side of the implement and the mechanical drive system employs a telescopic shaft coupled to a gear box located also on the left side of the implement but forward of the tongue pivot axis. In the '539 patent an implement is shown wherein the vertical axis about which the tongue pivots is centrally located along the frame and the gear box, also centrally located, is located forward of the tongue pivot axis. Among other things, a centrally located tongue permits operation of the implement on both sides of the tractor, as well as superior maneuverability for steering around obstacles and cutting square corners.
Other examples of prior art pull type harvesting implements with centrally located pivot tongues and mechanical drive systems with centrally located gear boxes are shown in U.S. Pat. Nos. 4,899,523, issued Feb. 13, 1990 in the name of Johny Frumholtz, et al, and No. 4,719,742, issued Jan. 19, 1988 in the name of Rino Ermacora, et al. In both these implements the drive shaft for the gear box is disposed within the tongue.
Another pull-type harvester configuration of the same general nature as those discussed above is the pivot tongue windrower shown in U.S. Pat. No. 5,272,859, issued on Dec. 28, 1993 in the name of Martin E. Pruitt, et al. This patent discloses a central gearbox mounted on the header such that the gearbox is movable relative to the implement frame. The gearbox is rotatable about a vertical axis so that the input shaft into the gearbox can generally follow the pivotal movement of the tongue, which pivots about a rearwardly located vertical axis. This eliminates the occurrence of sharp angles at the gear box under conditions where the tongue swings between its extreme angular positions.
To accomplish the coordinated movement of the rotation of the gearbox with the pivotal movement of the tongue, the '859 patent discloses a telescoping steering mechanism that interconnects the tongue and the gearbox such that the gearbox is rotated in response to swinging movement of the tongue relative to the implement frame. The telescopic action of the steering mechanism is operable to accommodate the changes in distance of the respective connecting points of the telescoping mechanism between the tongue and the gearbox, i.e., as the tongue swings from side to side, the distance changes between the different horizontally spaced pivot axes of the tongue and the gearbox. The telescopic action of the steering mechanism, along with a horizontal pivot or gimble, also allows the steering mechanism to follow the vertical movement of the header relative to the tongue without restricting movement of the header or the tongue.
This telescopic steering mechanism, as taught by the '859 patent, suffers from operational problems associated with vibration due to the loosely fitting telescopic parts and wear of the sliding parts. The implement, as can be seen in the drawings of the '859 patent, is provided with a rotatable cutting mechanism and a crop conditioning mechanism, which are typical of harvester components. The operation of harvesting components, such as these, provides a substantial amount of vibration within the implement. Since the steering mechanism is loosely constructed to permit the necessary relative pivotal movements of the header and the tongue, operational vibrations are not uncommon, leading to noise and wear in other elements and parts of the harvester. Furthermore, the looseness of the elements and the sliding action therebetween also cause substantial wear in the steering mechanism itself, resulting in increased likelihood of malfunction, or even worse, failure leading to costly downtime.
Additionally, the mechanism of the '859 patent is subject to side forces from the torque applied to the gearbox by the drive mechanism and the cutterbar forces within the crop harvesting header on which the rotatable gearbox is mounted. These external forces place a side load on the steering mechanism linkage and can result in a binding of the telescoping tubes forming the linkage, which results in a thrust load on the gearbox and the connecting apparatus, particularly when the header rises and the telescopic tubes telescope together. These telescoping tubes also present a hinge-like degree of freedom which can contribute further to vibrations in the implement.